Place all the mushroom sauce ingredients except sour cream into Slow Cooker and stir to combine.

Mix all ingredients for meatballs together in a bowl and shape into walnut size balls. Fry meatballs in a pan then add to sauce in the Slow Cooker. Cover and cook on LOW for 6-8 hours or HIGH for 2-4 hours. Fifteen minutes before serving, switch to HIGH and stir in the sour cream.